HVAC air filter monitor with sensor compensation

ABSTRACT

Sensor offsets for an air filter monitor installed in an HVAC system may be determined by measuring a sensor offset differential pressure value across an air filter when substantially no air flow exists through the air filter. The sensor offset differential pressure value obtained at or near zero flow may represent the sensor offset for the air filter monitor. The sensor offset differential pressure value may be used to compensate an un-compensated differential pressure value obtained during flow conditions.

TECHNICAL FIELD

This disclosure generally relates to HVAC systems that include an air filter, and more particularly, to methods and systems for monitoring the condition of the air filter and to provide an indication of when the air filter should be changed.

BACKGROUND

Heating, ventilation, and/or air conditioning (HVAC) systems are often used to control the comfort level within a building or other structure. Such HVAC systems typically include an HVAC controller that controls various HVAC components of the HVAC system in order to affect and/or control one or more environmental conditions within the building. Many HVAC systems, including many forced air HVAC systems, include an air filter to help remove dust and other pollutants from within the building and to protect the HVAC equipment from dust buildup which may negatively impact system performance. The air filter will become dirty over time, and as part of regular maintenance, the air filter should be changed. Continuing to run an HVAC system with an excessively dirty filter can reduce the efficiency of the HVAC system, and in some cases, can cause damage and/or reduce the expected lifetime of some of the HVAC components.

SUMMARY

The present disclosure relates generally to methods and systems for monitoring the condition of an air filter of an HVAC system, and to provide an indication of when the air filter should be changed. In one illustrative example, a method is provided for monitoring a status of an air filter of an HVAC system, where the HVAC system has a fan for driving air through the air filter of the HVAC system. The fan of the HVAC system may be turned “off” so that substantially no air is driven through the air filter. With the fan “off”, a sensor offset differential pressure value may be measured between an upstream side of the air filter and a downstream side of the air filter. The sensor offset differential value may be stored. Next, the fan of the HVAC system may be turned “on” so that air is driven through the air filter. With the fan “on”, an un-compensated differential pressure value may be measured between the upstream side of the air filter and the downstream side of the air filter. Then, a compensated differential pressure value may be determined by removing the sensor offset differential value from the un-compensated differential pressure value. In some cases, the compensated differential pressure value is determined by merely subtracting the sensor offset differential value from the un-compensated differential pressure value.

The status of the air filter may be determined based at least in part on the compensated differential pressure value. For example, if the compensated differential pressure value is less than a threshold value, the status of the air filter may be classified as “good”, while if the compensated differential pressure value is greater than a threshold value, the status of the air filter may be classified as “replace now”. Once the status of the air filter is determined, the status may be displayed on a display of an HVAC controller.

It is contemplated that a new sensor offset differential value may not need to be generated more than occasionally. That is, the same sensor offset differential pressure value may be used to compensate several or many un-compensated differential pressure values. In some cases, a new sensor offset differential value may be automatically generated occasionally, intermittently, at regular intervals, or at any other time. In some cases, a user may initiate the generation of a new sensor offset differential value. Also, it is contemplated that a new sensor offset differential value may be generated if a sensed temperature adjacent the air filter changes by more than a threshold amount.

An illustrative HVAC controller may include a controller, a memory coupled to the controller. The controller may be programmed to send a command to turn a fan of an HVAC system “off” so that substantially no air is driven through the air filter. With the fan “off”, the controller may obtain a sensor offset differential pressure value that is representative of a sensed pressure between an upstream side of the air filter and a downstream side of the air filter. The controller may store the sensor offset differential value in the memory.

The controller may send a command to turn the fan of the HVAC system “on” so that air is driven through the air filter. With the fan “on”, the controller may obtain an un-compensated differential pressure value that is representative of a sensed pressure between the upstream side of the air filter and the downstream side of the air filter. The controller may then determine a compensated differential pressure value by removing the sensor offset differential value from the un-compensated differential pressure value. The controller may determine the status of the air filter based, at least in part, on the compensated differential pressure value. In some cases, the controller may also display the status of the air filter on a display.

The preceding summary is provided to facilitate an understanding of some of the innovative features unique to the present disclosure and is not intended to be a full description. A full appreciation of the disclosure can be gained by taking the entire specification, claims, drawings, and abstract as a whole.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure may be more completely understood in consideration of the following description of various embodiments in connection with the accompanying drawings, in which:

FIG. 1 is a schematic view of an illustrative HVAC system located within a building or structure;

FIG. 2 is a schematic view of an illustrative HVAC controller;

FIG. 3 is a front view of an illustrative HVAC controller;

FIGS. 4-7 provide illustrative examples of various home screens that may be displayed upon the HVAC controllers of FIGS. 2 and 3;

FIGS. 8-9 provide illustrative examples of various screens that may be displayed by an HVAC controller showing a status of one or more components of the HVAC system;

FIG. 10 is a flow chart of an exemplary method of calibrating an HVAC system filter monitor using a clean air filter;

FIGS. 11A-11I provide illustrative examples of different screens that may be displayed by an HVAC controller following exemplary methods of calibrating an HVAC system filter monitor;

FIG. 12 is a flow chart of an exemplary method of calibrating an HVAC system filter monitor using a blocking panel;

FIG. 13A is a schematic view of an illustrative blocking panel used to at least partially block an air filter opening following the method outlined in FIG. 12;

FIG. 13B is a schematic view of an illustrative template used to size a blocking panel such as shown in FIG. 13A;

FIGS. 14A-14I provide illustrate examples of different screens that may be displayed by an HVAC controller following the exemplary method of calibrating an HVAC system filter monitor outlined in FIG. 12;

FIG. 15 is a flow chart of an example method of determining a sensor offset drift for an HVAC system filter monitor;

FIG. 16 is flow chart of an example method of monitoring a change in a physical parameter across an air filter during operation of the HVAC system;

FIGS. 17A-17E provide illustrative examples of different screens that may be displayed by an HVAC controller that is configured to display a user alert according to a user alert system; and

FIG. 18 is a flow chart of an example method of evaluating a new air filter.

While the disclosure is amenable to various modifications and alternative forms, specifics thereof have been shown by way of example in the drawings and will be described in detail. It should be understood, however, that the intention is not to limit aspects of the disclosure to the particular embodiments described. On the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the disclosure.

DESCRIPTION

The following description should be read with reference to the drawings wherein like reference numerals indicate like elements throughout the several views. The description and drawings show several embodiments which are meant to be illustrative of the claimed disclosure.

For convenience, the present disclosure may be described using relative terms including, for example, left, right, top, bottom, front, back, upper, lower, up, and down, as well as others. It is to be understood that these terms are merely used for illustrative purposes and are not meant to be limiting in any manner.

FIG. 1 is a schematic view of a building or other structure 2 having an illustrative heating, ventilation, and air conditioning (HVAC) system 4. While FIG. 1 shows a typical forced air type HVAC system, other types of HVAC systems are contemplated including, but not limited to, boiler systems, radiant heating systems, electric heating systems, or any other suitable type of HVAC system, as desired. The HVAC system 4 of FIG. 1 includes one or more HVAC components 6, a system of ductwork and air vents including a supply air duct 10 and a return air duct 14, and one or more HVAC controllers 18. The one or more HVAC components 6 may include, but are not limited to, a furnace, a heat pump, an electric heat pump, a geothermal heat pump, an electric heating unit, an air conditioning unit, a humidifier, a dehumidifier, an air exchanger, an air cleaner, and/or the like.

It is contemplated that the HVAC controller(s) 18 may be configured to control the comfort level in the building or structure by activating and deactivating the HVAC component(s) 6. The HVAC controller(s) 18 may be configured to control the HVAC component(s) 6 via a wired or wireless communication link 20. In some cases, the HVAC controller(s) 18 may be a thermostat, such as, for example, a wall mountable thermostat, but this is not required in all embodiments. In some embodiments, the one or more HVAC controllers 18 may include multiple zone controllers, each monitoring and/or controlling the comfort level within a particular zone in the building or other structure. An illustrative HVAC controller, which is not meant to be limiting in any way, is disclosed in: US Published Patent Application No. 20090140062, entitled “HVAC CONTROLLER THAT SELECTIVELY REPLACES OPERATING INFORMATION ON A DISPLAY WITH SYSTEM STATUS INFORMATION”; US Published Application No. 20090143880, entitled “HVAC CONTROLLER WITH CONTEXT SENSITIVE HELP SCREENS”; US Published Application No. 20090143918, entitled “METHOD AND APPARATUS FOR CONFIGURING AN HVAC CONTROLLER”; US Published Application No. 20090143916, entitled “HVAC CONTROLLER HAVING A PARAMETER ADJUSTMENT ELEMENT WITH A QUALITATIVE INDICATOR”; US Published Application No. 20090143879, entitled “HVAC CONTROLLER WITH PARAMETER CLUSTERING”; US Published Application No. 20090140056, entitled “HVAC CONTROLLER WITH QUICK SELECT FEATURE,” the entireties of which are incorporated herein by reference for all purposes.

In the illustrative HVAC system shown in FIG. 1, the HVAC component(s) 6 may provide heated air (and/or cooled air) via the ductwork throughout the building or other structure 2. As illustrated, the HVAC component(s) 6 may be in fluid communication with every room and/or zone in the building or other structure 2 via the ductwork 10 and 14. In operation, when a heat call signal is provided by the HVAC controller(s) 18, an HVAC component 6 (e.g., forced warm air furnace) may be activated to supply heated air to one or more rooms and/or zones within the building or other structure 2 via supply air ducts 10. The heated air may be forced through supply air duct 10 by a blower or fan 22. In this example, the cooler air from each zone may be returned to the HVAC component 6 (e.g., forced warm air furnace) for heating via return air ducts 14. Similarly, when a cool call signal is provided by the HVAC controller(s) 18, an HVAC component 6 (e.g., air conditioning unit) may be activated to supply cooled air to one or more rooms and/or zones within the building or other structure via supply air ducts 10. The cooled air may be forced through supply air duct 10 by the blower or fan 22. In this example, the warmer air from each zone may be returned to the HVAC component 6 (e.g., air conditioning unit) for cooling via return air ducts 14.

In some cases, the system of vents or ductwork 10 and/or 14 can include one or more dampers 24 to regulate the flow of air. For example, one or more dampers 24 may be coupled to one or more of the HVAC controllers 18 and can be coordinated with the operation of one or more HVAC components 6. The one or more HVAC controllers 18 may actuate dampers 24 to an open position, a closed position, and/or a partially open position to modulate the flow of air from the one or more HVAC components to an appropriate room and/or zone in the building or other structure. The dampers 24 may be particularly useful in zoned HVAC systems, and may be used to control which zone(s) receives conditioned air from the HVAC components 6.

In many instances, one or more air filters 30 may be used to remove dust and other pollutants from the air inside the building or other structure 2. In the illustrative example shown in FIG. 1, the air filter(s) 30 is installed in the return air duct 14 to filter the air prior to the air entering the HVAC component 6, but it is contemplated that any other suitable location for the air filter(s) 30 may be used. The presence of the air filter(s) 30 may not only to improve the indoor air quality, but may also may protect the HVAC components 6 from dust and other particulate matter that would otherwise be permitted to enter the HVAC component.

The air filter 30 may restrict the air flow within the HVAC system 4. The level of restriction may be characterized by, for example, a differential pressure drop across the air filter 30, a static pressure on one or both sides of the air filter, an air flow through the air filter, a current draw by the fan or blower 22 at a given fan speed, etc. The differential pressure drop across a new, clean air filter 30 may be low, but may increase as the air filter 30 catches dust and other particulate matter during the operation of the HVAC system 4. After a period of time, the differential pressure drop across the air filter may become significantly higher and replacement of the air filter 30 may be required to avoid potential damage to the HVAC system 4 and its various components.

The rate at which the air filter 30 may become dirty and needs replacement is often dependent on a variety of factors, some of which include the ductwork characteristics, equipment specifications, age and/or condition of the HVAC component(s) 6, the duty cycle of the HVAC component(s) 6, the type of filter, elapsed time, among others. One approach is to replace the air filter 30 on a regular basis (e.g. every three months). However, this may lead to excessive cost due to more frequent air filter replacement than needed, or may lead to a decrease in the efficiency and/or expected lifetime of the HVAC component(s) 6 in the case of less frequent replacements than needed.

In some cases, and as shown in FIG. 1, the HVAC system 4 may include an air filter monitor 34. The air filter monitor 34 may be configured to measure or detect a change in a given parameter that is related to the amount of flow restriction presented by the air filter 30, such as a static pressure or differential pressure drop across the air filter 30, an air flow through the air filter 30, the amount of current drawn by the fan or blower 22 at a given fan speed, etc. In some cases, the air filter monitor 34 may include a differential pressure sensor including a first pressure tap 38 a located in the return (incoming) air duct 14 and a second pressure tap 38 b located in the supply (outgoing) air duct 10. In some cases, the pressure tap 38 a may be located outside the return air duct 14 and may reference the ambient or atmospheric pressure. In some cases, the air filter monitor 34 may include a flow sensor that is capable of providing a measure that is related to the amount of air flow restriction through the air filter 30. For example, the air filter monitor 34 may be adapted to measure a flow rate, pressure, or a combination of flow rate and pressure through the air filter 30. These are just some examples.

The air filter monitor 34 may be configured to communicate with the HVAC controller 18 via, for example, a wired or wireless communication link 42. The air filter monitor 34 may communicate, relay or otherwise transmit data regarding the selected parameter related to the amount of flow restriction presented by the air filter 30 to the HVAC controller 18. The HVAC controller 18 may use the data from the air filter monitor 34 to evaluate the filter status. In some cases, the HVAC controller 18 may be configured to display information regarding the status of the air filter 30 to a user, based on data received from the air filter monitor 34. Also, and in some cases, the HVAC controller 18 may be configured to indicate to the user when a filter change may be necessary or desired.

FIG. 2 is a schematic view of an illustrative HVAC controller 18. In some instances, HVAC controller 18 may be a thermostat, but this is not required. In the illustrative embodiment of FIG. 2, HVAC controller 18 includes a controller/processor (e.g., microprocessor, microcontroller, etc.) 44 and a user interface 48. The processor 44 may be adapted to operate in accordance with an algorithm that controls or at least partially controls one or more HVAC components 6 of an HVAC system such as, for example, HVAC system 4 shown in FIG. 1. The processor 44 may, for example, operate in accordance with an algorithm that provides temperature set points, starting and/or ending times, and the like. In some cases, HVAC controller 18 may include a timer (not shown). The timer may be integral to the processor 44 or may be provided as a separate component.

In the illustrative embodiment, user interface 48 may be any suitable interface that permits controller 18 to display and/or solicit information as well as permit a user to enter data such as temperature set points, humidity set points, starting times, ending times, and the like. In some cases, user interface 48 may include a display and a distinct keypad. A display may be any suitable display. In some instances, a display may include or may be a liquid crystal display (LCD). If desired, user interface 48 may be a touch screen LCD panel that functions as both display and keypad. In some instances, a touch screen LCD panel may be adapted to solicit values for a number of operating parameters and/or to receive said values, but this is not required.

The illustrative HVAC controller 18 includes a memory block 52 that may be considered as being electrically connected to processor 44. Memory block 52 may be used to store any desired information, such as the aforementioned control algorithm, set points, differential pressure limits, and the like. Processor 44 may store information within memory block 52 and may subsequently retrieve the stored information. Memory block 52 may be any suitable type of storage device including, but not limited to, RAM, ROM, EPROM, flash memory, a hard drive, and the like.

In some cases, as illustrated, HVAC controller 18 may include a data port 56. Data port 56 may be configured to communicate with processor 44 and may, if desired, be used to either upload information to processor 44 or to download information from processor 44. Information that can be uploaded or downloaded may include values of operating parameters. In some instances, data port 56 may be used to upload a previously-created thermostat configuration into HVAC controller 18, thereby hastening the programming process. In some cases, data port 56 may be used to download a thermostat configuration that has been created using HVAC controller 18, so that the thermostat configuration may be used in other thermostats. In some cases, data port 56 may be used to upload and/or download information pertaining to an HVAC dealer or contractor. In some cases, data port 56 may be a wireless port such as a Bluetooth™ port or any other wireless protocol. In other cases, data port 56 may be a wired port such as a serial port, a parallel port, a CATS port, a USB (universal serial bus) port, or the like. In some instances, data port 56 may be a USB port and may be used to download and/or upload information from a USB flash drive. Other storage devices may also be employed, as desired.

FIG. 3 is a front view of HVAC controller 18 according to an illustrative embodiment. As depicted in FIG. 3, HVAC controller 18 may include a display 62 that is disposed within a housing 66. In some cases, display 62 may be a touch screen LCD display. If desired, display 62 may be a dot matrix touch screen LCD display. A dot matrix touch screen LCD display is a touch screen LCD that permits images such as letters, numbers, graphics, and the like to be displayed anywhere on the LCD, rather than being confined to predetermined locations such as is the case with a fixed segment LCD. Housing 66 may be formed of any suitable material, such as a polymeric material. In some cases, the housing 66 may be formed such that it defines data port 56 (FIG. 2). The housing 66 may also include suitable wiring and/or other electrical connections 68 such that the controller 18 may be electrically coupled to the building 2 and/or HVAC system 4.

In some cases, HVAC controller 18 may be configured to provide substantial display and/or programming functionality, but this is not required. In some cases, HVAC controller 18 may be configured to display a default display, also referred to herein as a home screen that is displayed by HVAC controller 18 when no other data entry is underway. FIG. 4 provides an example of a home screen 72 that may be displayed by HVAC controller 18. In some cases, home screens may include screens that can be accessed by a top level navigational menu. A home screen may, if desired, display one or more parameters relating to environmental conditions such as indoor and/or outdoor temperature and/or humidity, expected weather conditions, and/or the status of any equipment that is at least partially controlled by HVAC controller 18.

As shown in FIG. 4, the display 62 may display an illustrative home screen 72 that includes a navigational bar 76. Navigational bar 76 may be considered as providing top level navigation, but this is not required. In some cases, if desired, navigational bar 76 may include one or more of a HOME button 78, a FAN button 80, a SYSTEM button 82 and/or a MENU button 84. FIG. 4 is an example of a screen that may be displayed after a user has pushed HOME button 78.

In some cases, home screen 72 may be considered as having two or more regions. For example, home screen 72 may include a first region 86 and a second region 88. In some instances, first region 86 may be considered as displaying or otherwise providing primary information while second region 88 may be considered as displaying or otherwise providing secondary information. In some cases, primary information may be information that is considered to be more important, more interesting and/or more useful than secondary information. To illustrate, first region 86 may display one or more of a current temperature reading, a current indoor humidity, a schedule status, and the like. Second region 88 may display one or more of a date and time, an outdoor temperature reading, an outdoor humidity reading, an equipment status, and the like.

Home screen 72 may also include a third region 90 that may be used for displaying and/or adjusting a parameter value such as a parameter that is displayed within first region 86 of home screen 72. In some cases, for example, third region 90 may, as illustrated, display both a heating temperature set point and a cooling temperature set point, but this is not required. Third region 90 may include a first parameter 92, a first up arrow 94 and a first down arrow 96. Third region 90 may include a second parameter 98, a second up arrow 100 and a second down arrow 102. First parameter 92 may be adjusted up or down using first up arrow 94 and/or first down arrow 96, as appropriate. Second parameter 98 may be adjusted up or down using second up arrow 100 and/or second down arrow 102, as desired.

In some cases, home screen 72 may be configured to display information regarding the status of the air filter 30 (FIG. 1) of the HVAC system 4, and/or may be configured to indicate to a user when a filter change may be necessary or desired. For example, in FIGS. 5 and 6, information regarding the filter status may be displayed in the second region 88 of the home screen 72, but this is not required. In some cases, a filter status indicator 106 may be displayed in place of the information previously displayed in that second region 88 or the filter status indicator 106 may overlay the information that was previously displayed in the second region 88 of the home screen 72. In some cases, the filter status indicator 106 may be configured to display qualitative terms indicative of the current status of the air filter 30. As illustrated in FIG. 5, exemplary qualitative terms that may be used to indicate the status of the air filter may include, but are not limited to, “CLEAN”, “GOOD”, “DIRTY”, “CHANGE FILTER SOON”, “REPLACE FILTER SOON” “CHANGE AIR FILTER NEEDED”, “REPLACE AIR FILTER NOW” and “FILTER CHANGE REQUIRED”, among others. In other cases, as illustrated in FIG. 6, the filter status indicator 106 may be configured to display a graphical representation indicating the current status of the air filter 30. For example, a maximum number of bars displayed on a graph may represent that the status of the air filter 30 is good, while only a few bars displayed on a graph may indicate that a filter change is needed soon. A single bar or no bar at all displayed on a graph may represent that a filter change is need. In still other cases, as will be described in more detail below, the filter status indicator 106 may be color coded or may employ color-coded labels or indicators. In some cases, the filter status indicator 106 may be configured to produce an audible signal (e.g., intermittent beeps) that may indicate that a filter change is needed or desired.

In some instances, information regarding the filter status may be accessed by selecting the appropriate button, icon or tab provided, for example, along the navigational bar 76. For example, as shown in FIG. 7, the user may access information regarding the filter status by selecting STATUS button 108 provided along the navigational bar 76. Pressing the STATUS button 108 may result in a status screen 112 being displayed on the display 62 (FIG. 3). The status screen 112 may be configured to display information regarding the filter status.

In some cases, as illustrated in FIGS. 8 and 9, the status screen 112 also may be configured to display information regarding other HVAC system components. In some examples, the status screen 112 may include a first region 116 and a second region 120. The first region 116 may be configured to display a table 124 that contains select information regarding various system components of the HVAC system. Depending upon how much information the table 124 is configured to contain, the table 124 may be a scrollable table, but this is not required. In some cases, the table 124 may include at least one column and one row of information. For example, different system components are listed in a first column 128 labeled “EQUIPMENT.” The second column 132 labeled “SETTING” may provide the current setting for a select piece of equipment listed in the first column 128. The third column 136 labeled “STATUS” may provide the current status for a select piece of equipment listed in the first column. The table 124 can be configured to contain a different number of columns and row containing information about the HVAC system as desired. The second region 120 may include a scroll bar or sliding bar 140 that permits the user to move up and/or down within the table 124 to view select information regarding the system. For example, a system user may manipulate the sliding bar 140 up or down until information regarding the air filter is displayed.

In some cases, the table 124 may be configured to display qualitative information regarding the air filter 30. The identifier or label “AIR FILTRATION” or “AIR FILTER” may appear in the table 124 in the first column 128 labeled “EQUIPMENT”. This may indicate to the user that information pertaining to the air filter 30 appears in this row. Next, in the second column 132 labeled “SETTING”, information regarding the current setting pertaining to the air filter 30 may be displayed.

In some cases, as shown in FIG. 8, the table 124 may be configured to display qualitative terms in the third column 136 indicative of the current status of the air filter 30. Exemplary qualitative terms that may be used to indicate the status of the air filter include, but are not limited to, “CLEAN”, “GOOD”, “DIRTY”, “CHANGE FILTER SOON”, “REPLACE FILTER SOON” “CHANGE FILTER NEEDED”, “REPLACE FILTER NOW” and “FILTER CHANGE REQUIRED”, among others. In other cases, as illustrated by the example provided in FIG. 9, a graphical representation 144 indicating the current status of the air filter 30 may be displayed. For example, a maximum number of bars displayed on a graph may represent that the air filter 30 is clean, while only a few bars displayed on a graph may indicate that a filter change is needed soon. A single bar or no bar at all displayed on a graph may represent that a filter change is needed. In still other cases, color-coded labels or indicators may be used to indicate if a filter change is needed.

So that the HVAC controller 18 may display accurate information regarding the status of the air filter 30, the air filter monitor 34 may be calibrated. Calibrating the air filter monitor 34 may account for system variables/variations including, but not limited to, ductwork characteristics, equipment specifications, equipment set up, and the condition of the equipment, among others. Additionally, calibration may help ensure that the filter monitor 34 will work properly with the selected filter type and the particular HVAC system (e.g., HVAC system 4 in FIG. 1). The filter monitor 34 may be capable of working with a variety of filter types and a variety of HVAC systems, as well as different set-ups from different manufacturers. Calibration may also be used to provide a threshold value against which the parameter monitored (e.g., differential pressure drop across the air filter 30) may be evaluated.

FIG. 10 is a flow chart of an exemplary method 200 of setting an air filter change threshold value for an HVAC system. In such a case, a clean air filter may be installed in the HVAC system and used to determine and set an air filter change threshold value. The air filter change threshold value may then be used to calibrate and indicate the status of the filter, and in some cases, as discussed in further detail below, may trigger an alert to the user that the air filter 30 is dirty and may need to be replaced.

To determine and set an air filter change threshold value for the HVAC system), first a system user (e.g., installer or HVAC contractor) may install a clean air filter in the system. Next, in response to an indication that a clean air filter has been installed, the controller may instruct the HVAC system to operate in a selected mode or state (Block 210). The HVAC system may be operated in a mode or state in which the fan is “on” and drives air through the air filter. In some cases, this may be a “fan only” mode or state in which the heating and/or cooling element is “off” and only the fan is operated at a selected speed. In other cases, the HVAC system may be operated in a heating mode (e.g., HEAT 1) or a cooling mode (e.g., COOL 2). In another case, the HVAC system may be operated in a ventilation mode. In still other cases, the HVAC system may be operated in a humidifying mode or dehumidifying mode. Typically, the mode or state having the highest fan speed may be selected, but this is not always the case. In some cases, the mode may be selected based on which mode or state may provide the greatest negative impact on equipment life from a dirty filter.

While the HVAC system is operating in the selected mode, the controller (e.g., controller 18) may command or require the air filter monitor to measure the differential pressure across the clean air filter to obtain a system differential pressure measurement that is related to an amount of flow restriction presented by the clean air filter (Block 214). The differential pressure measurement may then be displayed to the user by the controller 18 on an appropriate screen of the display 62. In some cases the user may operate the HVAC system in various different states, obtaining a differential pressure or other measure related to an amount of flow restriction (e.g. air flow for a given fan speed) associated with the clean air filter for each state. However, each time a new measurement is obtained, it may replace the previous measurement, but this is not required. When so provided, the differential pressure measurement (or other measure related to an amount of flow restriction) may be based on the last state in which the HVAC system is operated, but this is not required.

Regardless of whether the user obtains a system differential pressure measurement from operating the HVAC system in a single or multiple modes or states, the system differential pressure measurement may be used to determine an air filter change threshold value (Block 218). The air filter change threshold value is indicative of an expected differential pressure across what is considered a dirty filter. The air filter change threshold value may be used to determine the status of the filter (e.g., clean or dirty). In some cases, the user may use their own knowledge of the system variables that may affect the air filter change threshold value for the specific application to determine or modify the air filter change threshold value. Alternatively, or in addition, a processor 44 may be programmed with an algorithm that may determine an air filter change threshold value using a measure related to the amount of flow restriction presented by the clean air filter. In some cases, the algorithm may rely on only the differential pressure measurement, but this is not required in all embodiments.

While not required, the algorithm used to determine the air filter change threshold value may employ one or more inputs that may be provided by the user. In some cases, the user may input information regarding the HVAC system components in response to one or more questions provided by the processor 44. For example, through the user interface 48, the user may input information regarding the HVAC system including, but not limited to, the MERV rating of the filter, the fan type (e.g., variable speed fan), the number of dampers, whether or not the HVAC system is a zone system, the location of the HVAC components, the age of the components, and/or the size of the building or dwelling, among others. Using the data provided by the user and/or the system a measure related to the amount of flow restriction presented by the clean air filter (e.g. differential pressure measurement), the controller 18 may calculate and sometimes subsequently display an air filter change threshold value for the HVAC system.

In some cases, the air filter change threshold value may be set such that it is about 25%-400% higher than that measured for the clean air filter. In some cases, the air filter change threshold value may be set such that it is about 5-300% higher than a differential pressure measurement associated with the clean air filter. In other cases, the air filter change threshold value may be set such that it is about 5-200% higher than a differential pressure measurement associated with the clean air filter. In other cases, the air filter change threshold value may be set such that it is about 5-150% higher than a differential pressure measurement associated with the clean air filter. In still yet other cases, the air filter change threshold value may be set such that it is about 1-50% higher than a differential pressure measurement associated with the clean air filter.

While the air filter change threshold value for indicating a dirty filter may be determined or adjusted by the user based on their own knowledge and/or by the controller using an algorithm for that purpose, the air filter change threshold value may nonetheless be limited by an upper threshold value and/or a lower threshold value. For example, the industry accepted standard for an air filter change threshold value indicating a dirty air filter may be about 0.6 inches of water (w.c.). In some cases, the air filter change threshold value for indicating a dirty filter determined by the user and/or the controller 18 may be limited to not exceed this or some other value. Similarly, the lower threshold value for the air filter change threshold value may be limited to be no less than the system differential pressure measurement obtained using a clean air filter. For example, if the system differential pressure measurement for a clean air filter is measured to be 0.1 w.c., an exemplary range in which the air filter change threshold value for indicating a dirty filter may be confined to a range of 0.2 w.c. to about 0.6 w.c., but this is not required.

In some instances, the air filter change threshold value may be stored in the memory 52 of the controller 18 (FIG. 2) (Block 222). In some cases, the processor 44 may be programmed with an algorithm that uses the air filter change threshold value stored in the memory 52 to determine the status of the air filter 30 by comparing, for example, a current differential pressure measurement to the air filter change threshold value, and based on the results of this comparison, may trigger an alert indicating that that the air filter is dirty and needs to be replaced.

In some cases, setting an air filter change threshold value using a clean air filter may be initiated by a user through the user interface 48 of the controller 18. FIGS. 11A-11H provide several illustrative examples of various display screens 230, 232, 234, 236, 238, 240, 242, and 244 that may be displayed by the controller 18 while setting an air filter change threshold value using a clean air filter.

To initiate the protocol for setting an air filter change threshold value, the user may first select the MENU button 248 displayed on the display screen 230 of the controller 18 (FIG. 11A). In response, a menu screen 232 may be displayed (FIG. 11B). The menu screen 232 may be configured to display a menu 250 listing at least one menu option 252. The menu 250 may display multiple menu options 252 in the form of a table 254. The table 254 may be a scrollable table in which case, a scroll bar 256 may also be provided to enable to the user to navigate up and/or down within the table 254 to view the different menu options 252. Exemplary menu options 252 may include a security settings menu option, a dealer information option, and/or installer options menu option.

In some cases, the calibration protocol may be accessed by selected the menu option 252 labeled INSTALLER OPTIONS. Selection of the INSTALLER OPTIONS menu option 252 may cause the controller 18 to display an INSTALLER OPTIONS menu screen 234 (FIG. 11C). The INSTALLER OPTIONS menu screen 234 may be configured to display one or more menu options 258 listing at least one installer option accessible via the INSTALLER OPTIONS menu screen 234. The menu options 258 may be provided in the form of a table 262. The table 262 may be a scrollable table in which case, a scroll bar 266 may be provided to enable the user to navigate up and/or down within the table 262 to view the different installer options available to the user. Exemplary installer options available to the user may include, but are not limited to, CREATE SETUP, VIEW/EDIT CURRENT SETUP, FILTER MONITORING CALIBRATION, and SET DIAGNOSTIC LIMITS, among others. The INSTALLER OPTIONS menu screen 234 may also be configured to display a PREVIOUS MENU button 270 that, upon its selection, may be programmed to return the user to the previous display screen, and a HELP button 272 that upon its selection may be configured to display a HELP menu listing various help topics to the user.

The protocol for setting an air filter change threshold value may be initiated by selecting the button 258 labeled FILTER MONITORING CALIBRATION on the INSTALLER OPTIONS menu screen 234. Selecting the FILTER MONITORING CALIBRATION button 258 on the INSTALLER OPTIONS menu screen 234 may cause a CALIBRATION menu screen 236 to be displayed (FIG. 11D). The CALIBRATION menu screen 236 may display one or more buttons 276 a, 276 b labeled with the different filter calibration methods that may be employed by the user to determine and set an air filter change threshold value. For example, as shown in FIG. 11D, the CALIBRATION menu screen 236 may be configured to display a first button 276 a labeled CLEAN FILTER CALIBRATION and a second button 276 b labeled BLOCKED FILTER CALIBRATION. In some cases, the CALIBRATION menu screen 236 may be configured to display a user prompt 278 that may prompt the user to select a calibration method from the different calibration method options that may be displayed by the CALIBRATION menu screen 236. The CALIBRATION menu screen 236 may be also configured to display a HELP button 280 and/or a CANCEL button 282 which, if selected, may return the user to the previous INSTALLER OPTIONS menu screen 234. Selection of the calibration method may be initiated by pressing either the CLEAN FILTER CALIBRATION button 276 a or the BLOCKED FILTER CALIBRATION button 276 b. In this example, as shown in FIG. 11D, the CLEAN FILTER CALIBRATION METHOD button 276 a is highlighted indicating to the user that the CLEAN FILTER METHOD option has been selected. Selection of the CLEAN FILTER CALIBRATION METHOD may be confirmed and/or initiated by pressing the NEXT button 286 displayed on the CALIBRATION menu screen 236.

Selection of the calibration method (e.g., the CLEAN FILTER CALIBRATION method), may cause a first user prompt screen 237 to be displayed (FIG. 11E). Here, in this example, upon selection of the CLEAN FILTER CALIBRATION method on the previous CALIBRATION menu screen 236, a first user prompt screen 237 may be displayed including a user prompt 287 prompting the user to select a mode in which to operate the HVAC system during the selected calibration method from at least two different operation mode options 289 a, 289 b, and 289 c that may be displayed by the first user prompt screen 287. For example, as shown in FIG. 11E, the user may select from a Heat Stage 1 mode, a Heat Stage 1 and 2 mode, or a Cool Stage 1 mode. The operation mode for calibration may be selected based on the mode that may provide the greatest negative impact on equipment life.

Selection of the desired mode may be initiated by pressing the button or icon 289 a, 289 b or 289 c associated with the desired mode of operation. In this example, as shown in FIG. 11E, button 289 b associated with Heat Stage 1 and 2 is highlighted indicating to the user that this is the selected mode in which the HVAC system will operate during the selected calibration method. Selection of the desired mode may be confirmed and/or initiated by pressing the NEXT button 286 displayed on the first user prompt screen 287. A button or icon 291 labeled BACK or RETEST may be displayed by the first user prompt screen 237 and may permit a user to return to this screen 237 or a previous screen when executing the selected calibration method in multiple modes.

After the mode in which to operate the HVAC system during the desired calibration method has been selected and confirmed, a second user prompt screen 238 may be displayed (FIG. 11F). Here, in this example, upon selection of the Heat Stage 1 and 2 mode on the previous user prompt screen 237, a second user prompt screen 238 may be displayed including a user prompt 288, prompting the user to install a clean air filter into the HVAC system. The user prompt 288 may also provide certain instructions to the user. In this example, as shown in FIG. 11F, the user prompt 288 may also instruct the user to press a button 292 labeled “Calibrate for Clean Filter Now” which may also appear on the first user prompt screen 238. Selecting the “Calibrate for Clean Filter Now” may finalize initiation of the calibration protocol and may cause the controller 18 to initiate a calibration protocol. The user prompt screen 238 may also be configured to display a BACK button 294 which may return the user to a previous screen (e.g., screen 236), a HELP button 296 which upon its selection may cause a HELP menu to be displayed, and/or a CANCEL button 298, which may cancel the selection of the desired calibration method (e.g., CLEAN FILTER CALIBRATION) and which may return the user to the previous screen (e.g., CALIBRATION menus screen 236) or a home screen.

Upon initiation of the selected calibration method, the display may be configured to display a STATUS screen 240 (FIG. 11G). The STATUS screen 240 may be configured to display a message 302 to the user indicating the current status of the calibration. The STATUS screen 240 may also indicate to the user that the controller 18 is busy.

Upon initiation of the clean air filter calibration method, the controller 18 may be configured to instruct or command the air filter monitor 34 to measure, for example, a differential pressure, across the clean air filter 30 installed by the user in response to the selection of the appropriate calibration method displayed by the first user prompt screen 238. Rather than a differential pressure measurement, it is contemplated that a static pressure measurement, an air flow measurement, or any other suitable measurement that is related to an amount of flow restriction presented by the air filter may be used. In some cases, after a measurement is made with the clean air filter, the controller 18 may be configured to display the measured value (e.g. differential pressure measurement value) on a third user prompt screen 242 (FIG. 11H). The third user prompt screen 242 may include multiple regions for conveying a variety of information to the user. For example, the third user prompt screen 242 may display a differential pressure measurement value obtained during calibration in a first region 306, and a user prompt 308 in a second region 310. The third user prompt screen 242 may be configured to display the selected calibration method in the first region 306 adjacent the differential pressure measurement value. The user prompt 308 may instruct or prompt the user to set or adjust an air filter change threshold value which may indicate a dirty filter based on, for example, the differential pressure measurement displayed in the first region 306. In some cases, the controller may automatically provide a default air filter change threshold value by, for example, adding an offset to the differential pressure measurement value.

In some cases, an adjustment bar 312 for adjusting or setting the air filter change threshold value may be provided in a third region 314 of the third user prompt screen 242 situated below the second region 310 containing the user prompt 308 and adjacent to the first region 306 displaying the differential pressure measurement value obtained during calibration. The adjustment bar 312 may be either a horizontal adjustment bar as depicted in FIG. 11H or may be a vertical adjustment bar. The adjustment bar 312 may include a slider 318 adapted to display a label 320 indicating a current quantitative setting of the air filter change threshold value. Additionally, the adjustment bar 312 may include a first button 322 and a second button 324 for increasing and decreasing the setting for the air filter change threshold value. In some cases, as the user increases and/or decreases the air filter change threshold value displayed by the controller using the first and/or second button 322, 324, the label 320 may indicate the current setting of the air filter change threshold value, and may continuously or incrementally change the value as it is increased or decreased. In some cases, the third user prompt screen 242 may also include at least one of a RETEST button 326, a HELP button 328, a CANCEL button 330, and a DONE button 332 located in a fourth region 334 of the display screen 242. Upon selection of the RETEST button 326, the controller 18 may be configured to re-execute the selected calibration method (e.g., clean filter calibration). The user may select the RETEST button 326 if they are dissatisfied with or question the differential pressure (or other) measurement that was obtained during the calibration that was just conducted. Selecting the HELP button 328 may cause a HELP menu to be displayed. Selecting of the CANCEL button 330 may cancel the current operation (e.g., adjustment of the threshold value) and may return the user to a previous screen (e.g., CALIBRATION menu screen 236) or a home screen (e.g., Home Screen 230).

After setting the air filter change threshold value, the user may select the DONE button 332 to indicate that that the air filter change threshold value has been set. This may cause the controller 18 to store the air filter change threshold value in its memory for reference during operation of the HVAC system. Additionally, this is the value upon which the controller 18 may use to determine the status of the air filter during subsequent operation of the HVAC system, and which may be used to trigger an alert to the user indicative of the status of the air filter.

Additionally, selection of the DONE button 332 may cause a confirmation screen 244 to be displayed (FIG. 11I). The confirmation screen 244 may include one or more user messages 336 that may indicate to the user that the threshold value has been set. The confirmation screen 244 may also be configured to display an OK button 338 prompting the user to acknowledge the message displayed by the confirmation screen 244. Upon selecting the OK button 338, the INSTALLER OPTIONS menu screen 234 (FIG. 11C) or the HOME screen 230 (FIG. 11A) may be displayed.

The air filter change threshold value also may be set using a blocked air filter (and/or blocking panel). When so provided, an at least partially blocked air filter (and/or blocking panel) may be used to determine and set an air filter change threshold value. Like above, the air filter change threshold value may then be used to indicate the status of the filter, and in some cases, may trigger an alert to the user that the air filter 30 is dirty and may need to be replaced.

FIG. 12 is a flow chart of a method 350 in which an at least partially blocked air filter (and/or blocking panel) is used to determine and set an air filter change threshold value for an HVAC system. An at least partially blocked air filter (and/or blocking panel) may be used in this method to simulate a dirty air filter, and in some cases, may provide a more accurate assessment of the performance of the HVAC system when the air filter is considered dirty.

To determine and set an air filter change threshold value for an HVAC system using an at least partially blocked air filter (and/or blocking panel), a system user (e.g., installer or HVAC contractor) may install a clean air filter in the system (Block 354). Next, the user may install a blocking panel into the system to at least partially block the clean air filter to simulate a dirty air filter (Block 354). The blocking panel may be a piece of cardboard, cardstock, poster board, or similar materials that may be inserted into the system to at least partially block the air filter in order to simulate a dirty air filter. The blocking panel may be installed in the system such that it at least partially blocks the return air side or the supply air side of the filter. The blocking panel may be sized using a template for that purpose. The template may be provided with the installation guide for the air filter monitor. In some cases, the blocking panel may also be provided with an installation guide. In some cases, a blocking panel may be used without a clean air filter installed. That is, the blocking panel may replace the air filter in the HVAC system, at least temporarily during calibration.

In some cases, a kit for installing an air filter monitor may include an installation guide or manual including instructions for installing and calibrating the air filter monitor. The kit may also include a template for sizing a blocking panel to achieve a desired reduction in air flow (% air flow blockage) in the HVAC system. In certain cases, a blocking panel may be initially provided with the kit. The template and the blocking panel may be discarded after successful installation and calibration of the air filter monitor.

FIGS. 13A and 13B are schematic diagrams of a blocking panel 378 and template 382 that may be used to size the blocking panel 378, respectively. In some cases the template 382 may be a part of and printed on the blocking panel 378. In other cases, the template 382 may be provided separately from the blocking panel. The template 382 may be used to size the blocking panel such that when the blocking panel 378 is inserted into the HVAC system, it results in at least a 25% air flow blockage, at least a 33% air flow blockage, at least a 50% air flow blockage, at least a 67% air flow blockage, or at least a 75% blockage. These are just some examples. The amount of blockage used to simulate a dirty filter may be selected by the user. In some cases, a 50% air flow blockage may be used.

In some cases, as shown in FIG. 13B, the template 382 may be a piece of paper or thin cardstock including at least one set of horizontal and vertical measurement lines 386 a-386 e that may be used to size the blocking panel 378 such that it results in a desired amount of air flow blockage. The template 382 may also include one or more labels 390 for indicating to the user the approximate percent air flow blockage that may result when a particular set of measurement lines 386 a-386 e are used to size the blocking panel 378. For example, as shown in FIG. 13B, the template 382 may include a first set of measurement lines 386 a that when used to size the blocking panel 378, may result in about a 25% air flow blockage. In some cases, the template 382 may include additional sets of measurement lines 386 b-386 e that when used to size a blocking panel, may result in at least a 33% air flow blockage, at least a 50% air flow blockage, at least a 67% air flow blockage, or at least a 75% blockage, respectively. In some cases, different sets of lines may be provided on the template, where each set of lines corresponds to a corresponding size air filter. This way, one blocking panel and template may be suitable for calibrating HVAC systems with different size air filters and/or different air flow blockages, as desired. In some cases, the blocking panel 378 may be sized by placing the template on the blocking panel 378 and using a cutting tool such as, for example, a pair of scissors, a razor blade, or an X-ACTO® knife to cut along the selected set of measurement lines 386 a-386 e.

Referring again to FIG. 12, after the blocking panel has been sized to achieve the desired amount of air flow blockage and inserted into the system, the user may select a system mode or state in which to operate the HVAC system (Block 362). The HVAC system may be operated in a mode or state in which the fan is “on” and drives air through the blocking panel and/or air filter. In some cases, this may be a “fan only” state or mode in which the heating and/or cooling element is “off” and only the fan is operated at a selected speed. In other cases, the HVAC system may be operated in a heating mode (e.g., HEAT 1) or a cooling mode (e.g., COOL 2). In another cases, the HVAC system may be operated in a ventilation mode. In still other cases, the HVAC system may be operated in a humidifying mode or a dehumidifying mode. Typically, the mode having the highest fan speed is selected, but this is not always the case. In some cases, the mode may be selected based on which mode may provide the greatest negative impact on equipment life from a dirty filter. The HVAC system may then be operated in the selected mode with the blocking panel to obtain, for example, a differential pressure or other measure related to an amount of flow restriction presented by the blocking panel (Blocks 358 and 362). In some cases, the user may operate the HVAC system in various different modes, obtaining a differential pressure or other measure related to an amount of flow restriction presented by the blocking panel for each mode. In some cases, each time a new measurement is obtained it may replace the previous measurement. Thus, the system differential pressure measurement associated with the at least partially blocked air filter may be based on the last mode in which the HVAC system is operated, but this is not required.

In some cases, after the system differential pressure measurement (or other measure related to an amount of flow restriction presented by the blocking panel) is obtained, the user may verify that the change in air temperature across the heat exchanger and the discharge air temperature are within an acceptable range suitable for the particular system (Block 370). This verification may be accomplished in any suitable way. For example, and in a first method, a return air sensor and a discharge air sensor may be connected to the HVAC controller 18. The HVAC system may then be configured to display the change in air temperature across the heat exchanger. In a second illustrative method, a discharge air sensor may be connected to the HVAC system controller and the HVAC system controller may be configured to display the discharge air temperature. The user may then measure the change in air temperature across the heat exchanger using standard HVAC air temperature measurement tools. In a third illustrative method, neither a return air temperature nor a discharge air temperature is utilized. Instead, the user may simply measure the change in air temperature across the heat exchanger and the discharge air temperature using standard HVAC air temperature measurement tools. These are merely illustrative.

If the change in temperature across the heat exchanger and/or the discharge air temperature are not within acceptable limits, then the user may adjust the amount of blockage by re-sizing the blocking panel or by using a different blocking panel, and may repeat the steps outlined in Blocks 362, 366, and 370. If the change in temperature across the heat exchanger and/or the discharge air temperature are found to be within the acceptable limits, the user may repeat the steps outlined in Blocks 362, 366, and 370 for multiple system modes, if desired. In some cases, the differential pressure measurement (or other measure related to an amount of flow restriction presented by the blocking panel) that is obtained may be based on the last mode in which the system was operated.

In some cases, the differential pressure measurement (or other measure related to an amount of flow restriction presented by the blocking panel) may be displayed to the user by the controller 18. It is contemplated that the system differential pressure measurement (or other measure related to an amount of flow restriction presented by the blocking panel) may be used, at least in part, to determine an air filter change threshold value (Block 366). Subsequently, the air filter change threshold value may be used to determine the status of the filter (e.g., clean or dirty). In some cases, the user may use their knowledge of the system variables that may affect the differential pressure threshold value for the specific HVAC system to determine or alter the air filter change threshold value, but this is not required.

In many cases, the air filter change threshold value may be set such that it is substantially equal to the measure that is related to the amount of air flow restriction presented by the at least partially blocked air filter. In this instance, the user may accept the measure as the default air filter change threshold value.

While the air filter change threshold value for indicating a dirty filter may be adjusted by the user based on their knowledge or by the controller using an algorithm for that purpose, the air filter change threshold value may be limited by an upper threshold value and a lower threshold value, as described above.

The air filter change threshold value may be stored in the memory 52 of the controller 18 (Block 370). In some cases, the processor 44 may be programmed with an algorithm that uses the air filter change threshold value stored in the memory 52 to determine the status of the air filter by comparing a current measure related to an amount of flow restriction presented by the air filter to the air filter change threshold value, and that, based on the results of this comparison, may trigger an alert indicating that that the filter is dirty and needs to be replaced. After the air filter change threshold value is set, the blocking panel may be removed from the HVAC system (Block 376).

The protocol for setting an air filter change threshold value using an at least partially blocked air filter may be initiated by a user through the user interface 48 of the controller 18 (FIGS. 1 and 2). FIGS. 14A-14G provide examples of various illustrative display screens 402, 406, 410, 414, 418, 422, and 426 that may be displayed by the controller 18 while setting an air filter change threshold value using an at least partially blocked air filter following a method such as, for example, described above with reference to FIG. 12.

To initiate the protocol for setting an air filter change threshold value using an at least partially blocked air filter (and/or blocking panel), the user may first select the MENU button 430 displayed on the display screen 402 of the controller (FIG. 14A). In response, a menu screen 406 may be displayed (FIG. 14B). The menu screen 406 may be configured to display a menu 434 listing at least one menu option 438. The menu 434 may display multiple menu options 438 in the form of a table 442. The table 434 may be a scrollable table in which case, a scroll bar 446 may also be provided to enable to the user to navigate up and/or down within the table 442 to view the different menu options 438. Exemplary menu options 438 may include a SECURITY SETTINGS menu option, a DEALER INFORMATION menu option, and/or INSTALLER OPTIONS menu option.

In some cases, the protocol for setting the air filter change threshold value may be accessed by selected the menu option 438 labeled INSTALLER OPTIONS. Selection of the INSTALLER OPTIONS menu option 438 may cause the controller to display an INSTALLER OPTIONS menu screen 410 (FIG. 14C). The INSTALLER OPTIONS menu screen 410 may be configured to display one or more menu options 450 listing at least one installer option accessible via the INSTALLER OPTIONS menu screen 410. The menu options 450 may be provided in the form of a table 454. The table 454 may be a scrollable table in which case, a scroll bar 458 may be provided to enable the user to navigate up and/or down within the table 454 to view the different installer options available to the user. Exemplary installer options available to the user may include, but are not limited to, CREATE SETUP, VIEW/EDIT CURRENT SETUP, FILTER MONITORING CALIBRATION, and SET DIAGNOSTIC LIMITS, among others. The INSTALLER OPTIONS menu screen 410 may also be configured to display a PREVIOUS MENU button 462 that upon its selection, may be programmed to return the user to the previous display screen or home screen 402, and a HELP button 464 that upon its selection may be configured to display a HELP menu listing various help topics to the user.

The protocol for setting the air filter change threshold value may be initiated by selecting the button 450 labeled FILTER MONITORING CALIBRATION on the INSTALLER OPTIONS menu screen 410. Selecting the FILTER MONITORING CALIBRATION button 450 on the INSTALLER OPTIONS menu screen 410 may cause a CALIBRATION menu screen 414 to be displayed (FIG. 14D). The CALIBRATION menu screen 414 may display one or more buttons 466 a, 466 b labeled with the different filter calibration methods that may be employed by the user to determine and set the air filter change threshold value. For example, as shown in FIG. 14D, the CALIBRATION menu screen 414 may be configured to display a first button 466 a labeled CLEAN FILTER CALIBRATION and a second button 466 b labeled BLOCKED FILTER CALIBRATION. In some cases, the CALIBRATION menu screen 414 may be configured to display a user prompt 470 that may prompt the user to select a calibration method from the different calibration method options that may be displayed by the CALIBRATION menu screen 414. The CALIBRATION menu screen 414 may be also configured to display a HELP button 474 and/or a CANCEL button 478 which, if selected, may return the user to the previous INSTALLER OPTIONS menu screen 410 or home screen 402. Selection of the calibration method may be initiated by pressing either the CLEAN FILTER CALIBRATION button 466 a or the BLOCKED FILTER CALIBRATION button 466 b. In this example, as shown in FIG. 11D, the BLOCKED FILTER CALIBRATION METHOD button 466 b is highlighted indicating to the user that the BLOCKED FILTER METHOD option has been selected. Selection of the BLOCKED FILTER CALIBRATION METHOD may be confirmed and/or initiated by pressing the NEXT button 482 displayed on the CALIBRATION menu screen 414.

Selection of the calibration method (e.g., the BLOCKED FILTER CALIBRATION method), may cause a user prompt screen 416 to be displayed (FIG. 11E). Here, in this example, upon selection of the BLOCKED FILTER CALIBRATION method on the previous CALIBRATION menu screen 414, a user prompt screen 416 may be displayed including a user prompt 483 prompting the user to select a mode in which to operate the HVAC system during the selected calibration method from at least two different operation mode options 484 a, 484 b, and 484 c that may be displayed by the user prompt screen 416. For example, as shown in FIG. 11E, the user may select from a Heat Stage 1 mode, a Heat Stage 1 and 2 mode, or a Cool Stage 1 mode. The operation mode for calibration may be selected based on the mode that may provide the greatest negative impact on equipment life.

Selection of the desired mode may be initiated by pressing the button or icon 484 a, 484 b or 484 c associated with the desired mode of operation. In this example, as shown in FIG. 11E, button 484 b associated with Heat Stage 1 and 2 is highlighted indicating to the user that this is the selected mode in which the HVAC system will operate during the selected calibration method. Selection of the desired mode may be confirmed and/or initiated by pressing the NEXT button 485 displayed on the user prompt screen 416.

After the mode in which to operate the HVAC system during the desired calibration method has been selected and confirmed, the controller 18 may be configured to measure a discharge air temperature and/or a change in air temperature across the heat exchanger to verify that these values are still within an acceptable range for the HVAC system when an at least partially blocked air filter is installed within the system. Additionally, the controller 18 may subsequently be configured to display a discharge air temperature verification screen 417 displaying the discharge air temperature and or change in air temperature across the heat exchanger in a first region 491 of the screen 417 (FIG. 11F). The screen 417 may include a user prompt 492 prompting the user to verify that the displayed discharge air temperature and/or change in air temperature is within an acceptable range for the HVAC system before final initiation of the BLOCKED FILTER CALIBRATION method. The BLOCKED FILTER CALIBRATION method may be initiated by selecting a button 493 labeled CALIBRATE FOR BLOCKED FILTER NOW provided on the discharge air temperature verification screen 417.

Upon initiation of the selected BLOCKED FILTER CALIBRATION method, the controller may be configured to display a STATUS screen 418 (FIG. 14G). The STATUS screen 418 may be configured to display a message 486 to the user indicating the current status of the calibration. The STATUS screen 418 may also indicate to the user that the controller is busy.

Upon initiation of the blocked filter calibration method, the controller 18 may be configured to measure, for example, a differential pressure via the air filter monitor 34 across the at least partially blocked air filter (and/or blocking panel) to obtain a measurement related to an amount of air flow restriction presented by the blocking panel. After a differential pressure measurement has been obtained by the controller, the controller 18 may be configured to display the differential pressure measurement value obtained during the blocked air filter calibration on a CALIBRATION RESULTS screen 422 (FIG. 14H). The CALIBRATION RESULTS screen 422 may include multiple regions for conveying a variety of information to the user. For example, the CALIBRATION RESULTS screen 422 may display the differential pressure measurement value obtained during calibration in a first region 490 and a user message 494 in a second region 498. The CALIBRATION RESULTS screen 422 may also be configured to display the calibration method in the first region 490 adjacent the differential pressure measurement value. The user message 494 may instruct or prompt the user to set or adjust an air filter change threshold value which may indicate a dirty filter based on the differential pressure measurement displayed in the first region 490.

An adjustment bar 502 for adjusting or setting the air filter change threshold value may be provided in a third region 506 of the screen 422 situated below the second region 498 containing the user message 494 and adjacent to the first region 490 displaying the differential pressure measurement value obtained during calibration. The adjustment bar 502 may be either a horizontal adjustment bar as depicted in FIG. 14H or may be a vertical adjustment bar. The adjustment bar 502 may include a slider 510 adapted to display a label 514 indicating a current setting of the differential pressure threshold value. Additionally, the adjustment bar 502 may include a first button 518 and a second button 522 for increasing and decreasing the setting for the differential pressure threshold value. In some cases, as the user increases and/or decreases the air filter change threshold value using the first and/or second button 518, 522 the label 514 indicating the current setting of the air filter change threshold value may also continuously or incrementally change to indicate the current setting of the air filter change threshold value as it is increased or decreased. In some cases, one or more qualitative labels 526 may be provided over the adjustment bar indicating in which direction the slider 510 may be moved indicating a clean or dirty filter. Exemplary qualitative labels include the terms CLEAN, DIRTY, CLEANER, DIRTIER, GOOD, BAD, OK, REPLACE, and REPLACE SOON, among others. Similarly, the buttons 518, 522 may also include directional arrows indicating in which direction the slider 510 may be moved to indicate a clean or dirty filter.

The CALIBRATION RESULTS screen 422 may also include at least one of a RETEST button 530, a HELP button 532, a CANCEL button 534, and a DONE button 538 located in a fourth region 542 of the display screen 422. Upon selection of the RETEST button 530, the controller may be configured to re-execute the selected calibration method (e.g., BLOCKED FILTER CALIBRATION). The user may select the RETEST button 530 if they are dissatisfied with or question the differential pressure measurement that was obtained by calibration that was just conducted. Selecting the HELP button 532 may cause a HELP menu to be displayed. Selecting of the CANCEL button 534 may cancel the current operation (e.g., adjustment of the threshold value) and may return the user to a previous screen (e.g., CALIBRATION menu screen 414) or a home screen (e.g., HOME screen 402).

In the example shown, the user may choose to either accept the differential pressure measurement as the default air filter change threshold value or may choose to adjust the differential measurement value to set the air filter change threshold value. After setting the air filter change threshold value, the user may select the DONE button 538 to indicate that that the air filter change threshold value has been selected. This may cause the controller to store the air filter change threshold value in its memory for reference during operation of the HVAC system. Additionally, this is the value upon which the controller 18 may use to determine whether or not an air filter is clear or dirty, and which may be used to trigger an alert to the user that may indicate that the filter needs to be replaced.

Additionally, selection of the DONE button 538 may cause a CONFIRMATION screen 426 to be displayed (FIG. 14I). The CONFIRMATION screen 426 may include one or more user messages 546 that may indicate to the user that the threshold value has been adjusted. The CONFIRMATION screen 426 may also be configured to display an OK button 552 prompting the user to acknowledge the message displayed by the confirmation screen 426. Upon selecting the OK button 552, the INSTALLER OPTIONS screen 410 (FIG. 14C) or the HOME screen 402 (FIG. 14A) may be displayed.

Referring again to FIG. 1, the air filter monitor 34 may be used to monitor the air filter 30 during operation of the HVAC system 4. For the purposes of this discussion, the air filter monitor 34 will be described as being adapted to measure a differential pressure across the air filter 30 between the supply air side and the return air side of the air filter 30. However, it must be understood, that the air filter monitor 34 may be adapted to measure a different physical parameter or to detect a change in a different physical parameter, such as air flow through the air filter, a static pressure on one or both sides of the air filter, current draw by the fan or blower 22 at a given fan speed, etc., as previously discussed.

In many cases, the air filter monitor 34, as described herein, may include a differential pressure sensor, which may experience a sensor offset and/or sensor drift over time and with temperature and/or over other environmental conditions. Sensor offset and/or sensor offset drift may decrease the accuracy of the differential pressure measurement. To improve accuracy of the differential pressure measured by the air filter monitor 34, sensor offset and/or sensor drift may be taken into account.

To determine sensor offset and/or sensor offset drift over time, the differential pressure between an upstream side and a downstream side of the air filter 30 may be measured at or near zero system pressure (e.g. with substantially no air flowing through the air filter). While differential pressure is used here as an example, it is contemplated that offsets for other sensors may be removed in a similar manner. It should be generally recognized that it is possible that a minimal amount of pressure may be present in the system, but that this minimal pressure may be considered to be negligible. In an ideal system, the differential pressure between the upstream side and the downstream side of the air filter 30 at zero system pressure should be equal to zero. However, this is not always the case for a variety of reasons. As such, the differential pressure measurement at zero pressure may be indicative of a sensor offset, which may drift with time and may reduce the accuracy of the differential pressure value. As such, and to improve the accuracy of the system, it is contemplated that the sensor offset may be measured from time to time and eliminated when determining the status of the air filter 30.

FIG. 15 outlines a method 600 of monitoring a status of an air filter (e.g., air filter 30) using a sensor offset differential pressure value for a differential pressure sensor (e.g., air filter monitor 34). While a differential pressure sensor is used here as an example, it is contemplated that sensor offsets from other types of sensors may be removed in a similar manner. As discussed above, the air filter monitor 34 may be in communication with the controller 18 via a wired or wireless communication link 42. In some cases, the controller 18 and/or processor 44 may be adapted to send a command to the HVAC system to turn off the fan or blower 22 so that substantially no air is driven through the air filter 30 (Block 602). Once the fan or blower 22 has been turned off, air stops circulating through the ductwork (e.g., supply air duct 10 and return air duct 14), and the system pressure may approach zero. Once the fan is “off” and the system pressure is at or near zero, the controller 18 and/or processor 44 may send a command to the air filter monitor 34 to measure a sensor offset differential pressure value between an upstream side of the air filter 30 and a downstream side of the air filter 30 (Block 604). The sensor offset differential pressure value may then be delivered to and stored within the memory 52 of the controller 18 (Block 608). In some cases, the controller may be configured to display the differential pressure measurement on the display, but this is not required. The controller 18 may then return the HVAC system 4 to a previous or selected operating mode in which the fan is turned “on” so that air is driven through the air filter (Block 610). In some cases, the previous or selected operating mode or state may be a cooling mode, a heating mode, a ventilation mode, a humidifying mode, a dehumidifying mode, and the like.

The sensor offset differential pressure value obtained at or near zero system pressure may be indicative of the sensor offset. For example, if the sensor offset differential pressure value measured at or near zero system pressure is 0.1 w.c., then the sensor offset can be considered to be equal to 0.1 w.c. The sensor offset differential pressure value may be monitored by the controller 18 as a function of time and/or ambient temperature. In some cases, when the sensor offset differential pressure value is obtained at or near zero system pressure, the controller 18 may also record the current ambient temperature and/or the amount of time lapsed from the last measurement of the sensor offset differential pressure value. Other physical parameters such as absolute pressure or humidity may also be monitored and recorded by the controller 18 as they may also affect sensor offset and/or sensor drift. This information may help the controller 18 to determine if the sensor offset differential pressure value is still accurate using an algorithm designed for this purpose. In some cases, the controller 18 may use the sensor offset differential pressure value to determine whether or not the current sensor offset differential pressure value calibration has expired. In such a case, the controller 18 may be configured to display a message to the user on the controller display 62 that the sensor offset differential pressure value calibration has expired and/or that a new sensor offset differential pressure value calibration may be necessary.

In some cases, the sensor offset differential pressure value may be obtained immediately or shortly after the initial system setup and calibration. In other cases, the sensor offset differential pressure value may be obtained at any time during operation of the HVAC system, such as occasionally from time-to-time, at regularly scheduled intervals according to an algorithm stored and executed by the controller 18, and/or in response to a user's request. In some cases, the sensor offset differential pressure value may be obtained on a monthly basis, a weekly basis, every five days, every three days, every 48 hours, every 24 hours, every 12 hours, every 6 hours, every 20 hours of fan operation, whenever the temperature changes by more than 2 degrees, etc., as desired.

In some cases, the controller 18 may be configured to operate the HVAC system in a state in which substantially no air flows through the system to generate a new sensor offset differential pressure value. The new sensor offset differential pressure value may replace a previously obtained sensor offset differential pressure value if the new value differs from the previously obtained value by a pre-determined amount. In other cases, the controller 18 may be configured to operate the HVAC system in a state in which substantially no air flows through the system to generate a new sensor offset differential pressure value if the temperature or ambient pressure changes by more than a predetermined threshold amount. The new sensor offset differential pressure value may then be stored in the memory of the controller. In certain cases, the controller may be configured to track the change in sensor offset differential pressure values over time; thereby quantifying the sensor offset drift. If the overall change in sensor offset differential pressure values is greater than a predetermined threshold for a predetermined number of measurements, then the controller maybe configured to alert the user that an error has occurred.

In some cases, the sensor offset differential pressure value may be used to more accurately calculate the differential pressure measurement used to evaluate the filter status. Often, this measurement may be obtained during operation of HVAC system, as will be described in greater detail below. In some cases, for example, after the sensor offset differential pressure value has been obtained; the controller 18 may send a command to turn the fan or blower 22 of the HVAC system “on” so that air flow is driven through the air filter. The controller 18 may then send a command or otherwise instruct the air filter monitor 34 to sense a differential pressure between the upstream side and the downstream side of the air filter 30 to obtain an un-compensated differential pressure value (Block 612). A compensated differential pressure measurement may be then obtained by, for example, subtracting the sensor offset differential pressure value (sensor offset) from the differential pressure measurement value according to the equation below (Block 614): ΔPcompensated=ΔPmeasured−ΔPsensor offset

The compensated differential pressure measurement (ΔPcompensated) may then be used, at least in part, to evaluate the status of the air filter 30 (Block 616). For example, in some cases, the controller may be programmed with an algorithm that compares the compensated differential pressure value to a predetermined air filter change threshold value to determine a current status of the air filter. In other cases, the controller may be programmed with an algorithm that compares a first compensated differential pressure measurement to a second compensated differential pressure measurement to determine a current status of the air filter. The controller may then be configured to display the status of the air filter to the user (Block 618).

In some cases, the controller 18 may be adapted to control the air filter monitor 34 such that the air filter monitor may periodically or occasionally monitor and measure the differential pressure across the air filter 30 during normal or routine operation of the HVAC system 4. The controller 18 and/or processor 44 may be programmed with an algorithm that uses this measurement to determine the status of the air filter (e.g., clean or dirty), which may trigger a user alert or perform any other suitable action, as desired.

FIG. 16 is a flow chart of an illustrative method 624 of monitoring a status of an air filter of an HVAC system during routine or normal operation of the HVAC system. In some cases, the status of the air filter is monitored by comparing a differential pressure measurement obtained when the HVAC system is operating in a predetermined state such as, for example, an air filter monitoring state. This method may be periodically or occasionally repeated during routine or normal operation of the HVAC system, with each new differential pressure measurement used, at least in part, to determine and/or update the status of the air filter. In some cases, the status of the air filter may be displayed by the controller and/or may be used to trigger a user alert.

In some cases, the controller 18 and/or processor 44 may be adapted to control the HVAC system equipment to place the HVAC system 4 in a an air filter monitoring mode before commanding the air filter monitor 34 to measure, for example, the differential pressure across the air filter 30 (Block 626). In some cases, the controller 18 and/or processor 44 periodically command the air filter monitor 34 to measure the differential pressure (e.g. at regular scheduled intervals), from time-to-time, and/or “on demand” in response to a user request. In some cases, the controller 18 may be adapted to place the HVAC system in the air filter monitoring mode such that the air filter monitor may measure the differential pressure across the air filter 30 on a monthly basis, a weekly basis, every five days, every three days, every 48 hours, every 24 hours, every 12 hours, or every 6 hours, every 20 hours of fan operation, or at any other suitable time, as desired. Alternatively, or in addition, the controller 18 may be programmed to place the HVAC system in the air filter monitoring mode and to command or instruct the air filter monitor 34 to measure the differential pressure in response to a user input or request (i.e., on demand).

In many cases, the same mode is used each time the air filter monitor 34 is requested to measure the differential pressure across the air filter 30. In some cases, the controller 18 may place the HVAC system in a “fan only” mode prior to commanding the air filter monitor 34 to measure the differential pressure across the air filter 30. In a “fan only” mode, all HVAC system equipment except for the fan may be placed in the “off state,” and for a zoned system, all dampers may be placed in the “open” position. In some cases, the heating or cooling element may be turned “off” In other cases, the heating element and/or cooling element may be turned on. In any event, the controller 18 may be adapted to turn on the fan or blower 22. The fan or blower 22 may be operated at the same fan speed each time a differential pressure measurement is made. For variable speed fans, the fan speed may be adjusted such that the fan is operated at the highest fan speed available, but this is not required. What may be desirable is that the fan speed setting should be consistent for each measurement, and all other variable (e.g. the on or off set of the heating and/or cooling element, the damper positions, etc., should also be constant. Thus, it may provide a more consistent and accurate differential pressure measurement over time.

The differential pressure across the air filter may be measured while the HVAC system is operating in the air filter monitoring (e.g. “fan only”) mode to obtain a differential pressure value or other value that is related to the amount of air flow restriction presented by the air filter (Block 628). The differential pressure value obtained while the HVAC system is operating in the air filter monitoring mode may be used, at least in part, to determine the current status of the air filter (Block 628).

The air filter monitor 34 may transmit or deliver data indicative of the differential pressure measurement to the controller 18, which may store the data in the controller memory 52. The controller 18 may be adapted to use this data to determine the status of the air filter 30. As discussed above, the differential pressure measurement used to determine the status of the air filter 30 may be compensated by subtracting a sensor offset differential value from the measured differential pressure value to produce a compensated differential pressure value which may be more accurate over time. In some cases, the controller 18 may be programmed with an algorithm that compares the differential pressure value from the air filter monitor 34 to an air filter change threshold value determined by calibrating the filter monitor using either a clean air filter or an at least partially blocked air filter (and/or blocking panel), as described herein, to determine the current status of the air filter, which may, in turn, be used to trigger a user alert.

After a differential pressure value associated with the HVAC system operating in the air filter monitoring has been obtained, the controller 18 may operate the HVAC system in a different state other than the air filter monitoring mode (Block 630). In this different operating state, at least one of the HVAC components may be operated in a different mode than it was while the HVAC system was operating in the air filter monitoring mode. In some cases, the different operating state may be a previous operating state of the HVAC system. For example, the controller 18 may operate the HVAC system in a cooling mode, a heating mode, a ventilation mode, a humidifying mode, a dehumidifying mode, and the like. After a period of time, the controller may again place the HVAC system in the air filter monitoring mode (Block 632). While the HVAC system is operating in the air filter monitoring mode, the controller may again command or request the air filter monitor 34 to obtain a second or subsequent differential pressure measurement associated with the air filter monitoring mode (Block 634). This second or subsequent value may be used, at least in part, to determine and/or update the status of the air filter after which, the controller may return the HVAC system to a different operating state other than the air filter monitoring mode. In some cases, the HVAC system may continue to operate in the different operating state according to a predetermined schedule. These steps may be occasionally repeated according to a predetermine schedule or in response to a user's request during the normal or routine operation of the HVAC system.

As previously discussed, the differential pressure measurement (or other measure related to the amount of air flow restriction presented by the air filter) may be used to evaluate the status of the air filter 30. In some cases, the controller 18 and/or processor 44 may be configured with an algorithm that compares the differential pressure measurement as measured by the air filter monitor 34 during operation of the HVAC system 4 to the air filter change threshold value. This comparison may then be used to determine the current status of the air filter.

In many cases, the controller 18 and/or processor 44 may be configured to trigger a user alert when the value of a measured physical parameter (e.g. differential pressure value) falls outside of the limits set for that particular parameter. In many cases, as discussed herein, the differential pressure across the air filter 30 may be monitored and detected by the air filter monitor 34. The differential pressure value that is measured by the air filter monitor 34 during operation of the HVAC system is related to an amount of air flow restriction presented by the air filter in the HVAC system. A dirty air filter will present more of an air flow restriction than a clean filter. The controller 18 may be programmed to receive the measured differential pressure value from the air filter monitor and compare the measured differential pressure value to the air filter change threshold value stored in the controller memory. As described above, the air filter change threshold value against which the measured differential pressure is evaluated may be determined using, for example, a clean air filter, an at least partially blocked air filter (and/or blocking panel) according to the methods as described herein, or any other suitable method as desired. If the differential pressure measurement as measured by the air filter monitor 34 during operation of the HVAC system 4 is greater than air filter change threshold value then, in some cases, the controller 18 and/or processor 44 may display the status of the air filter 30 on the user interface 48 (FIG. 2), provide an alarm, or perform any other suitable action, as desired.

In some cases, the controller 18 may be configured to display any one of a number of qualitative terms indicating the status of the air filter 30. Exemplary qualitative terms that may be used to indicate the status of the air filter include, but are not limited to, “CLEAN”, “GOOD”, “DIRTY”, “CHANGE FILTER SOON”, “REPLACE FILTER SOON” “CHANGE FILTER NEEDED”, “REPLACE FILTER NOW” and “FILTER CHANGE REQUIRED”, among others. In other cases, the controller 18 may be configured to display a graphical representation indicating the current status of the air filter 30. For example, a maximum number of bars displayed on a graph may represent that the air filter 30 is clean, while only a few bars displayed on a graph may indicate that a filter change is needed soon. A single bar or no bar at all displayed on a graph may represent that a filter change is needed. Additionally, color-coded labels or filter status indicators may be used to indicate if a filter change is needed. In some cases, the controller 18 may be configured to use a combination of the various indicators, as described herein, to indicate the status of the air filter 30. In still other cases, the controller 18 may be configured to sound an audible alert (e.g., intermittent beeps).

In some cases, the controller 18 may be configured to trigger a user alert depending upon the status of the air filter 30. In some cases, the user alert may be a part of a three-level user alert system configured to alert the user to the status of the air filter and, if necessary, alert the user to take action (i.e., change the filter, re-calibrate, check connections, calibration expired, etc.). The illustrative three-level user alert system may, in some cases, combine qualitative terms with a color code to alert the user to the filter status. In some cases, the three-level alert system may employ a stoplight metaphor. For example, when the differential pressure value across the air filter remains below the air filter change threshold value, the status displayed by the controller may be labeled as “Good” and a green color may be displayed. When the differential pressure value across the air filter remains repeatedly at or above the air filter change threshold value, sometimes for at least two or more consecutive measurements or for a predetermined amount of time, the controller 18 may display a label “Change Filter Soon”, along with the color yellow. In some cases, when the filter status changes from “Good” to “Change Filter Soon”, the controller 18 may initiate a timer that expires a predetermined amount of time later. The air filter monitor 34 may continue to monitor the differential pressure during this period, but this is not necessary. The controller 18 may include a “snooze” function, which may permit the user to temporarily remove or delay the “Change Filter Soon” user alert for a short period of time. If the user does not replace the filter during this snooze period, the controller may trigger a new user alert.

In some cases, once in the “Change Filter Soon” state, after a predetermined period of time set by the controller 18, the controller 18 may change the filter status from “Change Filter Soon” to “Change Filter Now”, and may change the color from yellow to red. In some cases, the “snooze” function may no longer be available to the user.

FIGS. 17A-17E provide illustrative screens 652, 654, 656, 658, and 670 that may be displayed by a controller (e.g., controller 18) configured with a three-level user alert system, as described above. FIGS. 17A, 17B, and 17D provide illustrative home screens 652, 654, and 658, each including a navigational bar 672, a first region 676, a second region 680, and a third region 684. In some cases, the controller may be configured to display the air filter status 688 in the first region 676 of the home screens 652, 654 and/or 658 as depicted in FIGS. 17A, 17B, and 17D. The air filter status 688 may be displayed in only a portion of the first region 676 or may be displayed such that it covers the entire first region 676 of the home screen 652, 652, and/or 658. Note, the air filter status 688, when present, may replace the information that was previously displayed in the first region 676 of the home screen.

FIG. 17A shows an illustrative home screen 652 in which the filter status may be indicated as “Good.” In some cases, the qualitative term displayed on the screen may be color coded (e.g. green). In other cases, the first region 676, either in part or in whole, may be color coded (e.g. green, yellow, red) to indicate the status of the filter. As indicated above, when the qualitative term indicates that the filter status is “Good”, the associated color code may be green.

FIG. 17B provides an illustrative home screen 654 that may be displayed when the controller determines that a filter change may be needed soon. A filter status indicator 688 indicative of the air filter status may appear in the first region 676 of the home screen 654. As described above, when provided, one of many exemplary terms may be used to indicate the status of the air filter. In some cases, the air filter status indicator may display the term “Replace Air Filter Soon.” Additionally, the air filter status indicator 688 may be color coded. Here, the color associated with the filter status indicator 688 may be yellow. As shown in FIG. 17B, the air filter status may cover the entire first region 678 and may block other useful information such as, for example, the current date and time from the user's view. This may annoy the user, prompting the user to take action more quickly than they otherwise would if they could more easily ignore the user alert.

In some cases, the filter status indicator 688 may include a button, label, or tab 690 labeled “Press for more info.” In response to the user selecting the button 690 labeled “Press for more info”, the controller may display a first user notification screen 656 as depicted in FIG. 17C. The first user notification screen 656 may include a user notification bar 692 which may include navigational arrows 694 a and 694 b. The first user notification screen 656 may be configured to display a user notification or message 698 in a region 702 below the user notification bar 692. Additional user notifications or messages (not shown) may be displayed by using the navigational arrows 694 a and 694 b provided with the user notification bar 692. The user notification bar 692 may also be configured to identify which message is displayed and how many user notifications messages are available. For example, the user notification bar 692 of FIG. 17C may indicate that the user notification message that is displayed is the first of three available user notification messages.

The first user notification screen 656 additionally may include at least one additional button for accessing more additional information or another function of the controller. In some cases, the first user notification screen 656 includes at least a delay button 706 which, when selected, initiates a snooze function that may temporarily remove the user alert displayed in the first region 676 of the home screen 654 (FIG. 17B) for a predetermined period of time. The delay button 706 may be labeled “Snooze”, “Remind me later”, “Delay”, “Dismiss”, and the like. Additionally, the first user notification screen 656 may also include a button 708 labeled “View Filter Sizes” or “View Filter Info” that, when selected, may display the filter size, MERV rating(s), and or other information regarding the air filter. The first user notification screen 656 may also include at least one acknowledge button 710 that, when selected, may enable the user to acknowledge the user message 698 displayed on the screen 656. Button 710 may be labeled “OK”, “Acknowledge”, “Done”, “Enter”, or any other suitable label as desired. Additionally, selecting button 710 may return the user to the previous home screen such as, for example home screen 654 (FIG. 17B).

FIG. 17D provides an example of a home screen 658 that is displayed when the controller determines that a filter change is necessary now. A filter status indicator 688 indicative of the air status may appear in the first region 676 of the home screen 658. In this case, the air filter status indicator 688 may display the term “Replace Air Filter Now”, “Filter Change Required”, or any other suitable label. Additionally, the air filter status indicator 688 may be color coded. Here, the color associated with the filter status indicator 688 may be red. As shown in FIG. 17D, the air filter indicator status 688 may cover the entire first region 676 and may block other useful information such as, for example, the current date and time from the user's view.

In some cases, the filter status indicator 688 may include a button, label, or tab 690 labeled “Press for more info.” In response to the user selecting the button 690 labeled “Press for more info”, the controller may display a second user notification screen 670 as illustrated by FIG. 17E. The second user notification screen 670 may be configured to display a user notification or message 714 that may indicate to the user that the air filter needs to be changed. Additional information that may be useful to the user may be included in the user notification message 714. The second user notification screen 670 may also include at least one additional button for accessing more additional information or another function of the controller. In some cases, the second user notification screen 670 includes at least a delay button 706 which, when selected, initiates a snooze function and may temporarily remove the user alert displayed in the first region 676 of the home screen 654 (FIG. 17B). The delay button 706 may be labeled “Snooze”, “Remind me later”, “Delay”, “Dismiss”, and the like. In some cases, when the controller determines that a filter change is necessary now, the delay button 706 may be no longer available to the user for selection (e.g. it may not be provided, grayed out, or otherwise not available for selection).

Like above, the second user notification screen 670 may also include a button 708 labeled “View Filter Sizes” or “View Filter Info” that, when selected, may display the filter size and/or MERV rating(s) of the filter that may be used with the HVAC system and a button 709 that, when selected, may display dealer information. The second user notification screen 670 may also include at least one acknowledge button 710 that, when selected, may enable the user to acknowledge the user message 714 displayed on the screen 670. Button 710 may be labeled “OK”, “Acknowledge”, “Done”, or “Enter.” Additionally, selecting button 710 may also return the user to the previous home screen such as, for example, home screen 658 (FIG. 17D).

The user may replace the filter in response to a user alert displayed by the controller. Upon replacement of the filter, the user may select a button 718 labeled “New Filter Installed” or “Test New Filter” found on the user notification screens 656 and 670 as illustrated in FIGS. 17C and 17E. The user may access either of the user notification screens 656 and 670 by selecting the button 690 labeled “Press for More Info” found on the filter status indicator 688 or by selecting the appropriate button from the menu navigation bar 672 that is displayed on the home screen 652, as illustrated in FIG. 17A.

In some cases, upon selection of button 718 labeled “New Filter Installed,” the controller 18 may be configured to obtain a differential pressure measurement to verify that in fact a clean filter has been installed in the system. Additionally, the controller 18 may be configured to display a user alert if the differential pressure measurement obtained after a new filter has been installed is not below the air filter change threshold value. The differential pressure measurement obtained after a new filter has been installed may not be below the air filter change threshold value if a more restrictive filter (e.g., higher MERV rating) was installed, or if the user did not actually install a new and/or clean filter.

In some cases, the HVAC system 4 may be operating according to a predetermined schedule and/or mode in which the air filter monitor 34 may periodically perform a new differential pressure measurement. For example, prior to the filter change, the HVAC system may be operating in a heating mode, a cooling mode, a ventilation mode, a humidifying mode, a dehumidifying mode, and the like. In other cases, the HVAC system may be off However, upon indication by the user that a new air filter has been installed, the controller 18 may be configured to obtain a new differential pressure measurement shortly (within a few minutes) after installation of the new air filter 30. This may provide relatively immediate feedback to the user regarding the installation of the new filter.

FIG. 18 is a flow chart of a method 750 of evaluating a new air filter. In some cases, a user may install a new filter in the HVAC system. In some cases, the controller 18 may accept an input from the user indicating that a new air filter has been installed (Block 752). In response to the input, the controller 18 may be configured to automatically operate the HVAC system 4 in an air filter verifying state or mode before commanding the air filter monitor 34 to measure the differential pressure across the air filter 30 (Block 754). In many cases, prior to being operated in the air filter verifying state, at least one of the HVAC components was operated in a different state. In some cases, the controller 18 may operate the HVAC system in a “fan only” mode in the air filter verifying state. In such a “fan only” mode, all HVAC system equipment other than the fan may be placed in the “off state,” and for a zoned system, all dampers may be placed in the “open” position.

Once the HVAC system 4 is in the air filter verifying mode, the controller 18 may command the air filter monitor 34 to obtain a differential pressure measurement across the air filter. The differential pressure measurement that is obtained may be related to an amount of air flow restriction presented by the new air filter. The air filter monitor 34 may transmit or deliver data indicative of the differential pressure measurement across the new air filter 30 to the controller 18. The controller 18 may receive the differential pressure measurement data from the air filter monitor and may store the data within the controller memory 52 (Block 756). The controller 18 and/or processor 44 may be adapted to use this data, at least in part, to determine whether or not a proper new filter has been installed (Block 758). In some cases, the differential pressure measurement used to determine whether or not a proper new filter has been installed may be adjusted by subtracting a sensor offset value from the measured differential pressure to produce a compensated differential pressure value obtained with the new filter installed. In some cases, the controller 18 and/or processor 44 may be programmed with an algorithm that compares the differential pressure measurement obtained using the new filter to a predetermined threshold value to determine whether or not a proper new air filter has been installed. In some instances, the predetermined threshold value may be determined using a clean air filter or an at least partially blocked air filter (e.g. blocking panel) according to one of the methods, as described herein.

If the differential pressure measurement obtained using a new filter is less than the predetermined threshold value, the controller 18 may automatically return the HVAC system to its previous operating mode. In some cases, the controller 18 may display a message to the user confirming the installation of the new filter was successful, and may then display a home screen (Block 760). If the differential pressure measurement obtained using the new filter is above the predetermined threshold value, the controller 18 may display an error message or other user alert. The user may then repeat the steps as outlined in Blocks 752, 754, 756, and 758 using the same or a different filter. The user may also access information about the appropriate filter(s) for the HVAC system through the user interface, as described above. This information may be useful in determining if the correct type of filter for the HVAC system has been installed. However, if the user simply re-installed the dirty filter, the controller may again display an error message or other user alert.

The HVAC system 4 may still continue to operate with a dirty filter; however, this may not provide adequate protection to the HVAC system components and may shorten their life expectancy. Regular replacement of the air filter may be recommended.

Having thus described several illustrative embodiments of the present disclosure, those of skill in the art will readily appreciate that yet other embodiments may be made and used within the scope of the claims hereto attached. Numerous advantages of the disclosure covered by this document have been set forth in the foregoing description. It will be understood, however, that this disclosure is, in many respect, only illustrative. Changes may be made in details, particularly in matters of shape, size, and arrangement of parts, without exceeding the scope of the disclosure. The disclosure's scope is, of course, defined in the language in which the appended claims are expressed. 

What is claimed is:
 1. A method of monitoring a status of an air filter of an HVAC system, wherein the HVAC system has a fan for driving air through the air filter of the HVAC system, the method comprising: a) turning the fan “off” so that substantially no air is driven through the air filter; b) with the fan “off”, measuring a sensor offset differential pressure value between an upstream side of the air filter and a downstream side of the air filter; c) storing the sensor offset differential value; d) turning the fan “on” so that air is driven through the air filter; e) with the fan “on”, measuring an un-compensated differential pressure value between the upstream side of the air filter and the downstream side of the air filter; f) determining a compensated differential pressure value by removing the sensor offset differential value from the un-compensated differential pressure value; g) determining the status of the air filter based, at least in part, on the compensated differential pressure value; and h) displaying the status of the air filter on a display of an HVAC controller.
 2. The method of claim 1 further comprising displaying the sensor offset differential value on a display of an HVAC controller.
 3. The method of claim 1 further comprising displaying the status of the air filter on a display of an HVAC controller.
 4. The method of claim 1, wherein the compensated differential pressure value is determined by subtracting the sensor offset differential value from the un-compensated differential pressure value.
 5. The method of claim 1 further comprising repeating steps (e)-(h) for two or more times using the same sensor offset differential pressure value.
 6. The method of claim 5 further comprising repeating steps (a)-(c) to generate a new sensor offset differential pressure value after steps (e)-(h) have been repeated for two or more times.
 7. The method of claim 5 further comprising repeating steps (a)-(c) to generate a new sensor offset differential pressure value at regular intervals.
 8. The method of claim 5 further comprising repeating steps (a)-(c) to generate a new sensor offset differential pressure value upon a user request.
 9. The method of claim 1 further comprising occasionally repeating steps (a)-(c) to generate a new sensor offset differential pressure value, and storing the new sensor offset differential pressure value only if it differs from the previous sensor offset differential pressure value by a threshold amount.
 10. The method of claim 1, wherein the HVAC system is operated in a heating mode before steps (a)-(h), and returning to operating the HVAC system in the heating mode after steps (a)-(h).
 11. The method of claim 1, wherein the HVAC system is operated in a cooling mode before steps (a)-(h), and returning to operating the HVAC system in the cooling mode after steps (a)-(h).
 12. The method of claim 1, wherein the HVAC system is operated in a ventilation mode before steps (a)-(h), and returning to operating the HVAC system in the ventilation mode after steps (a)-(h).
 13. The method of claim 1 further comprising obtaining a measure of temperature, and repeating steps (a)-(c) to generate a new sensor offset differential pressure value if the temperature changes by more than a threshold amount.
 14. A method of monitoring a status of an air filter of an HVAC system, wherein the HVAC system has a fan for driving air through the air filter of the HVAC system, the method comprising: operating the HVAC system in a heating mode, cooling mode or ventilation mode; occasionally entering an air filter monitoring mode, wherein the air filter monitoring mode includes: turning the fan of the HVAC system “off” so that substantially no air is driven through the air filter; with the fan “off”, measuring a sensor offset differential pressure value between an upstream side of the air filter and a downstream side of the air filter; storing the sensor offset differential value; occasionally entering an air filter monitoring mode, wherein the air filter monitoring mode includes: turning the fan “on” so that air is driven through the air filter; with the fan “on”, measuring an un-compensated differential pressure value between the upstream side of the air filter and the downstream side of the air filter; determining a compensated differential pressure value by removing the stored sensor offset differential value from the un-compensated differential pressure value; determining the status of the air filter based, at least in part, on the compensated differential pressure value; displaying the status of the air filter on a display of an HVAC controller.
 15. The method of claim 14 further comprising returning the HVAC system to the heating mode, cooling mode or ventilation mode from the air filter monitoring mode.
 16. The method of claim 15 further comprising re-entering the air filter monitoring mode after operating the HVAC system in the heating mode, cooling mode or ventilation mode.
 17. An HVAC controller for monitoring a status of an air filter of an HVAC system, wherein the HVAC system has a fan for driving air through the air filter of the HVAC system, the HVAC controller comprising: a controller; a memory coupled to the controller; a display coupled to the controller; wherein the controller is programmed to: send a command to turn the fan of the HVAC system “off” so that substantially no air is driven through the air filter; with the fan “off”, obtain a sensor offset differential pressure value that is representative of a sensed pressure between an upstream side of the air filter and a downstream side of the air filter; store the sensor offset differential value in the memory; send a command to turn the fan of the HVAC system “on” so that air is driven through the air filter; with the fan “on”, obtain an un-compensated differential pressure value that is representative of a sensed pressure between the upstream side of the air filter and the downstream side of the air filter; determine a compensated differential pressure value by removing the sensor offset differential value from the un-compensated differential pressure value; determining the status of the air filter based, at least in part, on the compensated differential pressure value; and displaying the status of the air filter on a display.
 18. The HVAC controller of claim 17, wherein the controller is further programmed to display the sensor offset differential value on the display.
 19. The HVAC controller of claim 18, wherein the compensated differential pressure value is determined by subtracting the sensor offset differential value from the un-compensated differential pressure value. 